It is named after Giovanni Cassini, the discoverer of Iapetus; 'Regio' is a term used in planetary geology for a large area that is strongly differentiated in colour or albedo from its surroundings.
Cassini-Huygens | Giovanni Domenico Cassini | Cassini–Huygens | Cassini | Regio | DB Regio | Cassini (disambiguation) | Regio (Swiss railway train) | Igor Cassini | Nadia Cassini | An engraving of the '''Paris Observatory''' during Cassini's time. The tower on the right is the "''Marly Tower''", a dismantled part of the Machine de Marly |